A brake system provided for example in a large automobile includes an air brake that uses compressed air supplied from an air compressor as an energy source for braking. This air brake includes a pushrod that pushes a brake shoe outward and a brake chamber provided to drive the pushrod. The brake chamber houses a diaphragm that deforms in response to supply of the compressed air to push the pushrod against the brake shoe (see Patent Document 1, for example).
This brake chamber may include a service brake chamber for braking during running of a vehicle that applies brakes on wheels by compressed air, and a spring brake chamber operating as a parking brake that is arranged side by side with the service brake chamber. In the spring brake chamber, a spring is contracted by the pressure of compressed air so that a piston inside the chamber does not push the pushrod in a non-braking state. In a braking state, the compressed air is removed so that the pushing force of the spring acts on the pushrod, thereby activating the brake.
Specifically, in the spring brake chamber, the pressure of compressed air contracts the spring so that the piston inside the chamber does not push the pushrod in a non-braking state. In a braking state, the compressed air is removed so that the pushing force of the spring acts on the piston to make the piston push the pushrod, thereby activating the brake.
If air leakage occurs in a supply route along which compressed air is supplied to the spring brake chamber, the spring keeps pressing the piston, specifically the brake is kept activated and this activation cannot be canceled. Therefore, the spring brake chamber is provided with a release bolt with which the spring brake is cancelled manually (see Patent Document 1, for example). Specifically, rotating the release bolt shifts the piston to a brake release position, thereby allowing the spring brake to be cancelled.